The present invention relates to synthesis of polar, non-aqueous dispersion polymers and their stabilization. More particularly, the invention relates to polymeric microparticles that find utility in coating applications for enhancing the ability to attain high solids content, to provide rheology control, or to control pigment orientation.
The book entitled DISPERSION POLYMERIZATION IN ORGANIC MEDIA, edited by K. E. J. Barrett, John Wiley and Sons, 1975 describes the synthesis of various non-aqueous dispersion polymers and their stabilization. Although aliphatic hydrocarbons, such as heptane or cyclohexane have been mostly used as the dispersion medium, polar solvents such as fluoro or chloro substituted hydrocarbons, esters, ketones and even alcohols have been used, if required, depending upon the polymer composition and its solubility.
For example, Barrett's text describes non-aqueous dispersion polymerization of acrylonitrile in non-polar solvent such as hexane and polar solvent such as methylethyl ketone. The dispersant used is a "comb" type copolymer of methyl methacrylate containing poly (12-hydroxystearic acid) pendant side chains and randomly distributed pendant polymerizable double bonds. Further, Barrett also describes polymerization of acrylonitrile in ethanol which is a polar solvent using chain transfer reaction to graft initially formed acrylonitrile particles onto dispersant.
Barrett's text also refers to unsuccessful attempts to synthesize poly acrylic or poly methacrylic acid in aliphatic hydrocarbons using various dispersants. He reasons the failure is due to hydrogen bonding of acid monomers in non-polar medium. Later, by the use of polar organic diluents such as esters or ketones, stable dispersions of poly acrylic acid were prepared. In both instances, however, the dispersant contained polymerizable unsaturation, and stabilization was achieved by grafting with the pendant unsaturation.
Prior art however does not describe the synthesis of poly 2-hydroxyethyl acrylate dispersion.